Anatomically shaped osteochondral constructs for articular cartilage repair

Few successful treatment modalities exist for surface-wide, full-thickness lesions of articular cartilage. Functional tissue engineering offers a great potential for the clinical management of such lesions. Our long-term hypothesis is that anatomically shaped tissue constructs of entire articular layers can be engineered in vitro on a bony substrate, for subsequent implantation. To determine the feasibility, this study investigated the development of bilayered scaffolds of chondrocyte-seeded agarose on natural trabecular bone. In a series of three experiments, bovine chondrocytes were seeded in (1) cylindrical bilayered constructs of agarose and bovine trabecular bone, 0.53 cm2 in surface area and 3.2 mm thick, and were cultured for up to 6 weeks; (2) chondrocyte-seeded anatomically shaped agarose constructs reproducing the human patellar articular layer (area=11.7 cm2, mean thickness=3.4 mm), cultured for up to 6 weeks; and (3) chondrocyte-seeded anatomically shaped agarose constructs of the patella (same as above) integrated into a corresponding anatomically shaped trabecular bone substrate, cultured for up to 2 weeks. Articular layer geometry, previously acquired from human cadaver joints, was used in conjunction with computer-aided design and manufacturing technology to create these anatomically accurate molds. In all experiments, chondrocytes remained viable over the entire culture period, with the agarose maintaining its shape while remaining firmly attached to the underlying bony substrate (when present). With culture time, the constructs exhibited positive type II collagen staining as well as increased matrix elaboration (Safranin O staining for glycosaminoglycans) and material properties (Young's modulus and aggregate modulus). Despite the use of relatively large agarose constructs partially integrated with trabecular bone, no adverse diffusion limitation effects were observed. Anatomically shaped constructs on a bony substrate may represent a new paradigm in the design of a functional articular cartilage tissue replacement.